Takedown bows



. Nov. 10, 1964 H. W. GROVES TAKEDOWN BOWS Filed Oct. 19, 1960 UnitedStates Patent 3,156,239 TAKEDQWN BOWS Harold W. Groves, 1821 SomervellSt. NE., Albuquerque, N. Mex. Filed Get. 19, was, Ser. No. 63,551 2Claims. (CL 124-23) This invention relates to two piece demountable, oras they are more commonly known, takedown archery bows. Moreparticularly, this invention is directed to a two piece scarf jointedtakedown archery bow.

Archery bows have a length about equal to the height of the archer withthe result that the bow is an awkward and cumbersome object to carry ortransport. Nevertheless, the rigidity of the middle part of a bow is soessential that no jointed bow has hitherto met the requirements of theart to the extent of finding favor with demanding archers. This rigiditymust be obtained in a joint which is easy to assemble with automaticalignment of the two parts. The joint must be so strong that there willbe no detectable flexing at full draw or any other time. In addition,the mechanism provided for joining the two bow parts must not requireany modification in the shape of the bow and it must not add anyappreciable or discernable weight to the bow.

The objective of this invention is to provide an archery bow which meetsall the foregoing requirements. The manner in which this is accomplishedwill be clearly understood from the following description havingreference to the drawing which is made a part of this specification andin which:

FIGURE 1 is an outline showing of the disjointed bow and the partsprovided for alignment and securing.

FIGURE 2 is side fragmentary view partly in section showing the bowjoint assembled but not tightened.

FIGURE 3 is a view similar to FIGURE 2 but showing the joint fullytightened.

Referring to the drawing, FIGURE 1, a completed bow having the joint ofthis invention is shown in exploded view. A scarf joint is providedbetween limbs A and B in the riser portion and just below or in thelower part of the handle and lying in a plane which fore and aftinclines downwardly from the belly side to the back side and which fromside to side is normal to a median line through the limbs.

Provision for precision alignment of the two bow limbs is made by a pairof leader pins mating in accurately located opposed sockets 13 and 15.The leader or pilot pins 11 are desirably permanently afiixed in one oftheir respective sockets. A threaded socket 17 is provided in the upperlimb approximately in the center of the joint to cooperate with a capscrew 19 seated in a bore 21 and counter bore 23. Provision is made inthe configuration of the joint as will be seen in the more detailedshowing of FIGURE 2 such that when the joint is assembled and tightenedfor use it is absolutely rigid with no discernable flexing or workingwhatever.

Referring now to FIGURE 2, a more detailed showing of the jointdesignated generally by the numeral 9 is made. This joint liessymmetrically about the median plane it). The following description hasparticular reference to the built up laminated bow comprising an innercore of wood and outer layers of glass fiber or glass cloth. Many ofsuch bows are custom made to a particular order specifying size anddraw. Where this is the case, the bow must be in essentially completedform before the joint may be made. The first step in processing thejoint is to lay out on the finished bow blank the proper angle for thesaw cut to part the bow. The bow is next mounted in a drilling devicesuch as a drill press with the angle of the joint line at right anglesto the drill. The bore is made in the approximate center of 'ice thecontemplated joint and is started on the surface of the nether limb. Thebore is drilled to a depth approximately on the opposite side of thejoint plane. The values herein given are not intended to be limiting buthave been found to be adequate in practice for a 66 inch bow of 40 pounddraw. The center bolt is of inch diameter and has a length of 1 /2inches in the stem portion. The center bore is therefore of inchdiameter in this embodiment.

The bow blank is next counter bored to a depth of inch to allow for areceiving recess for the cap screw head as shown at 19 and 23 in FIGURE2.

The bow blank is next removed from the drilling device and is accuratelyparted on the previously marked joint plane by a sawing operation. Thebore in the upper or handle limb is enlarged and tap-threaded tocooperate with a threaded metal insert 2-5. The threaded receptacle inthe bow blank is provided with a layer of strong adhesive which hasgreat binding strength to both wood and metal such as an epoxy resin.The bushing is promptly screwed into the receptacle and the adhesiveallowed to set.

The opposing surfaces of the joint are next provided with glass fiberplates. Thecombined thickness of these plates is equal to the width ofthe saw kerf made during the sawing operation. The butt plates areobtained by cementing a glass fiber layer of cloth to each limb jointportant feature of my improved joint in that it is the means by whichWorking and flexing in the joint are prevented and the originalcharacteristics of the bow are maintained.

The amount of hollow grinding necessary will depend upon the particularwood in the bow riser and the material of the butt plates. The amount ofhollow grinding in any particular case can be determined withconventional engineering stress analysis with the criteria, however,that the joint must be closed, i.e., no gap must appear when theclamping bolt is properly tightened, and this amount of compression ofthe outer fibers of the bow limbs contiguous the joint on the back sideof the bow must be at least equal to what the tension would be at fulldraw if no joint were present. This is equivalent to a pre-compressionon the belly side of the joint such that it is equal at least to what itwould have been at full draw if no joint were present and multiplied bya factor of two if the joint is present at right angles to the length ofthe bow and the joining bolt is in the middle. The reason for this isthat the length of the moment arm in the joint is reduced to one half ofits original length. As a matter of practice, it is not feasible to makea right angle joint and instead a scarf joint is utilized. The length ofthe moment arm, i.e., the distance between bolt and abutting surfaces ofthe bow limbs on the belly side is one half the thickness of the bow atthe joint times the secant of the angle between the scarf and thedirection of thickness of the bow at the joint. It is preferred that theangle of the scarf be at 45 degrees and accordingly the length of themoment arm is one half the thickness times 1.4 or more convenientlystated as .7 T where T stands for the thickness of the bow at the joint.

From the above analysis and a determination of the modulus of elasticityof the material abutting the joint, be it rosewood, beefwood or otherhardwood, the amount of compression on the belly side at full draw canbe readily determined and from this determination, the

J amount of hollow grinding necessary in the abutting surfaces of thejoint is established.

It is desirable that the joint be hollow ground an amount which is inexcess of the bare necessary extent and I prefer a safety factor of atleast two in this respect. For example, in a thirty inch limb length inthe nether limb of a forty pound bow having an overall length of 66inches, I provide a hollow grind of 0.0075 inch and a like amount ofhollow grinding in the abutting surface of the longer limb. The totalclearance in this example is therefore 0.015 inch. This value allows forgive or set in the material of the joint and the bolt socket and resultsin a joint of integrity for the life of the how.

The bow is next reassembled and clamped tightly by bolt 19, meanwhilemaking certain that the two sections of the bow are in perfect alignmentat the joint. The bow is mounted in a drilling device such as a drillpress with the plane of the joint at right angles with the drill. Thetwo pilot pin sockets 13-15 are drilled and accurately reamed to asqueeze fit with the pins. The bow sections are next disassembled andthe pins are forced into one set of the sockets so provided. A strongbinding cement such as a urac or epoxy cement is previously applied tothe sockets to which the pins are permanently afiixed. The second pairof sockets are lapped or carefully reamed to a snug slip fit with theremaining or free ends of the pins.

The bow joint is inconspicuous in the assembled bow as is seen in FIGURE3. The open ends of the pin sockets are preferably plugged with hardwood plugs cemented in place. The bow blank is now ready for the finalprocedures such as adjusting, finishing and polishing as is the customin the art.

While I have shown and described the fundamental novel features of theinvention as applied to a preferred embodiment, it is understood thatthere may be various omissions and substitutions and changes in theprocedures, forms and details in the making of and in the deviceillustrated by those skilled in the art without departing from thespirit of the invention. It is my intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

I claim:

1. A takedown bow having two limbs joined in a riser section, a gripfitting handle portion in the middle of the riser section, said gripfitting handle portion being configured to the natural grip of the humanhand, a scarf joint in said riser portion commencing proximate thehandle portion lower end at the bellyface and extending through theriser section on a descending plane to the back face, said scarf jointbeing provided by a sawing operation of the unitary bow blank, acomposition plate having a thickness equal to half the saw kerf afiixedto the joint surface of each limb, at least one of said plates beinggradually diminished in thickness from the fore and aft end portions tothe middle thereof, a clamp bolt seat in the bottom limb aligned withthe perpendicular to the joint and being located in the middle of thejoint substantially, a clamp bolt threaded socket afiixed in the upperlimb and aligned with the bolt seat when the limbs are in assembledalignment, a pair of guide pin sockets transfixing said joint andlocated in the opposing surfaces of the limbs in spaced relation foreand aft the middle of the joint, a pair of guide pins adapted to seat insaid guide pin sockets to align the limbs when assembled, and a boltadapted to engage said bolt seat and bolt socket to compressedly joinsaid limbs and said plates with consequent compression of the fore andaft outer portions of the limbs.

2. The takedown bow of claim 1 in which said scarf joint lies in a planeof degrees approximately to the direction of elongation of the bow.

References Cited in the file of this patent UNITED STATES PATENTS114,138 Hersey Apr. 25, 1871 1,082,062 Aine Dec. 23, 1913 1,720,269Fullerton July 9, 1929 2,228,823 Helm Jan. 14, 1941 2,353,134 AndersonJuly 11, 1944 2,457,793 Bear Dec. 28, 1948 2,514,638 Grenier July 11,1950

1. A TAKEDOWN BOW HAVING TWO LIMBS JOINED IN A RISER SECTION, A GRIPFITTING HANDLE PORTION IN THE MIDDLE OF THE RISER SECTION, SAID GRIPFITTING HANDLE PORTION BEING CONFIGURED TO THE NATURAL GRIP OF THE HUMANHAND, A SCARF JOINT IN SAID RISER PORTION COMMENCING PROXIMATE THEHANDLE PORTION LOWER END AT THE BELLYFACE AND EXTENDING THROUGH THERISER SECTION ON A DESCENDING PLANE TO THE BACK FACE, SAID SCARF JOINTBEING PROVIDED BY A SAWING OPERATION OF THE UNITARY BOW BLANK, ACOMPOSITION PLATE HAVING A THICKNESS EQUAL TO HALF THE SAW KERF AFFIXEDTO THE JOINT SURFACE OF EACH LIMB, AT LEAST ONE OF SAID PLATES BEINGGRADUALLY DIMINISHED IN THICKNESS FROM THE FORE AND AFT END PORTIONS TOTHE MIDDLE THEREOF, A CLAMP BOLT SEAT IN THE BOTTOM LIMB ALIGNED WITHTHE PERPENDICULAR TO THE JOINT AND BEING LOCATED IN THE MIDDLE OF THEJOINT SUBSTANTIALLY, A CLAMP BOLT THREADED SOCKET AFFIXED IN THE UPPERLIMB AND ALIGNED WITH THE BOLT SEAT WHEN THE LIMBS ARE IN ASSEMBLEDALIGNMENT, A PAIR OF GUIDE PIN SOCKETS TRANSFIXING SAID JOINT ANDLOCATED IN THE OPPOSING SURFACES OF THE LIMBS IN SPACED RELATION FOREAND AFT THE MIDDLE OF THE JOINT, A PAIR OF GUIDE PINS ADAPTED TO SEAT INSAID GUIDE PIN SOCKETS TO ALIGN THE LIMBS WHEN ASSEMBLED, AND A BOLTADAPTED TO ENGAGE SAID BOLT SEAT AND BOLT SOCKET TO COMPRESSEDLY JOINSAID LIMBS AND SAID PLATES WITH CONSEQUENT COMPRESSION OF THE FORE ANDAFT OUTER PORTIONS OF THE LIMBS.